Protease inhibitors are used as therapy in HIV patients and have been reported to cause elevations in plasma triglycerides, cholesterol, and glucose, and rarely to induce severe hypertriglyceridemia, pancreatitis, and diabetes mellitus with insulin resistance, excess fat deposition, and lipodystrophy. Our aims are to measure fasting Serum cholesterol (C), triglyceride (TG), remnant lipoprotein (RLP) C and TG, low density lipoprotein (LDL) C, high density lipoprotein C, lipoprotein(a), apolipoproteins A-I and B, apo E genotype, homocysteine, free fatty acids, glucose, insulin, and blood pressure. We will also assess smoking status, carotid artery wall thickness by ultrasound, and coronary artery calcification by computerized tomography in our prospective cohort of 400 HIV patients whose nutritional status is being evaluated and who are taking a variety of antiviral agents including protease inhibitors. Comparisons will be made on and off inhibitors and also longitudinally, and with controls. Our comparison group are participants in the Framingham Offspring Study who have had all the same parameters measured (n=3250). HIV patients who become hyperlipidemic on protease inhibitors will be treated with either gemfibrozil or atorvastatin. We will also examine the effects of protease inhibition in Hep G2 and CaCo2 cells with or without supplementation with fatty acids and cholesterol on lipoprotein assembly and secretion and apolipoprotein, LDL receptor, and microsomal transfer protein (MTP) gene expression. The effects of protease inhibition on lipoprotein metabolism and aortic foam cell formation will also be assessed in F1B hamsters on chow and on diets high in cholesterol and saturated fat. In addition, using a primed constant infusion in the constantly fed state and deuterated leucine, the secretion and catabolism of apoB-48 and apoB-100 within lipoproteins will be determined by GC/MS analysis and multicompartmental modeling in the presence or absence of protease inhibition with ritonavir in 10 males and 10 female HIV patients. We will test the following hypothesis: 1) protease inhibitors increase triglyceride and cholesterol by increasing RLP; 2) elevated RLP leads to increased carotid wall thickness and coronary calcification; 3) these increases can be ameliorated with diet, gemfibrozil and/or atorvastatin treatment; 4) in cell culture these RLP increases are elated to enhanced secretion of apo B-100 due to less intracellular degradation, and excess cellular lipid content; 5) in hamsters there are increased RLP in serum in animals on the atherogenic diet, especially with protease inhibition, and this leads to increased aortic foam cell formation; 6) in humans protease inhibition causes increased triglyceride-rich lipoprotein apo B-100 secretion. This research should define the nature of the problem, its mechanism, and methods for treatment wit regard to the hyperlipidemia induced by protease inhibitors in HIV patients.